Exposure meter



July 7,]1936. N. MILLER 2,046,646

EXPOSURE METER Filed May 16, 1952 2 Sheets-Sheet lv lll l f s H- Pl Pn eA2 Il @2l @s 2 Inventor @mam @MIA July 7, 1936. N, MILLER 2,046,646

EXPOSURE METER Filed May 16, "1932 z sheets-sheet 2 [nvm :or

Patented July 7,1 1936 v .;UNlTEo STATES Parlzlrl 1 OFFICE 'lhepupillaryopening of the eye, as is well,

known, Varies with the intensity of the light entering the eye and is caused by the automatic contraction or dilation of the iris, which tendsto maintain a constant light energy on the retina. Tile diameter of thepupil v'aries from 2 to 8 millimeters, and the objects of the presentillvention are to'provide a device for the estimation oflight-intensities by the measurements of the .pupillary diameters,whichimay be expressed in terms of exposure times required inphotography.

In `the present invention a, magnied virtual image of the'pupil, formedby a convex lens in front of it, is viewed by means o f a pair ofadjacent reflectors, wllich are pivotally mounted so that the anglebetween them-may be varied at will. When the angle between thereflectors is other than'zero, each reflector will reflect a 'distinctimage from the virtual image rays of the convex lens. If the anglebetween the reflectors is varied, the two reiiected images are caused tomove, one relative to the other, and it is possible by this means tobring two dialnetrically opposed points of the pupil into coincidence.The angularity of the reectors. corresponding to this relationofcoincidence is dependent upon the size of the pupil. so that, themagnitude of this angle is a measure of the pupil diameter and therefore.of the light intensity entering the eye.

Asis well known, the distance of distinct vision varies with diil'erentindividuals and it is desirable in a device of this kind, to bring theobject of observation (that is the pupil) into sharp focus. This isaccomplished by moving the pupil toward or away from the convex lensuntil the images appear most distinct. However, such an `adjustmentalters the position 'as' well as the size of i the virtual image formedby the convex lens, and this in turn requires a diierent angle between4@the reilectors for the condition of coincidence above described. Inthe present invention automatic compensating means are provided, wherebythe coincidence of the images is unaffected by the 4 adjustments offocusing, that is, the indicated .for near, normal or far vision.

The contraction or dilation of the iris.V follows la. well deiinedgeneral law, but the size of the measure of the pupil diameter'will bethe same" conveniently making such an adjustment are provided and willbe explained in connection with the drawings.

If one eye is more strongly illuminated than the other, equality ofpllpillary areas results, due 5 to the consensual action of the eyes.Thus, if

. the instrument, herein disclosed, is placed in front of the pupil ofthe right-eye, the left eye may be directed toward the object thebrightness of which is to be measured,'and the size of the pupil 10 ofthe right eye will be 'influenced by the light proceeding from theobject, even though the right eye is obscured by the instrument.4

Fig. 1 represents in a schematic diagram, the geometric relations of thevarious elements of the 15 optic system. Y

Fig. 2 shows the rays bywhich animage of a point of the iris is formed.

Fig. 3 shows the relations of the images ol.' the pupil corresponding tonear, normal and far vi- 20 sion. Fig. 4 representsthe relations of theimages of Fig. 3 after compensation.

Fig. 5 shows the manner of using the instrument.

Fig. 6 shows the front view of the device when not in use. y

Fig. 7 is a diagrammatic view of the pupil images in alignment.

Fig. 8 shows a top view of the inside mecha, 30

Fig. 12 is a section on line I'2, I2 of Fig." 8. 40'

Fig. 13 is a section on line |3, I3 Fig..8.

Fig. 14 is a partial section on line |I, Il Fig. 8.

In Fig. 1, l represents the convex lens in front of the pupil and n andr2 represent the two ad` jacent reflectors. In this diagram the anglebetween the reilectbrs is zero, so that they will re-' iiect only asingle image. The position and the size ofthe pupil for normal vision'is shown at Az and a virtual enlarged image of this is formed by thelens l at Ac'; lthis image Az'is reproduced by reectors 1:1 and r2 atthe position Az" on the optic axis; The rays forming the virtual imageof A2" are, however, reflected back to the lens z, cc that the lens win:crm c anal v imml innige far vision are at A1 and A3, and thecorresponding virtual'imagles are at A1' and A3', which are reproducedby reflection at A1" and A3". The

corresponding final images formed by the lens and observed by the eye,are shown at A1'Y and Aa" respectively. A

In Fig.\2 the reectors r1 and r2 are shown at anangle, and the virtualimage 'P' Q is reproduced by reflector r1 at P1" Q1" and by reector r2a't P2" Q2", the points Q1" and P2" corresponding to points P and Q ofthe pupil being in coincidence, and hence points Q1'" Pa" of the finalimages, which are observed bythe eye, are likewise in coincidence,appearing as shown in Fig. 7. The rays proceeding from the point Q ofthe pupil, pass through the lens l to the reector r1 and are reflectedback through lthe lens into the eye. All of the rays proceeding from Qand reected from the reector 1'1 appear to issue from the final imagepoint Q1", and all such rays are included in the angle P Q1'" A. Asimilar set of rays correspond to the point P and reflector r2, and toall other points of the pupil.

` In Fig. 3, P2 Q2 represents the position of the pupil corresponding tonormal vision, and the angle between the reflectors r1 and 12 is such,that the corresponding image points Q12" and P22" are in coincidenceupon the axis. If now, in the process of focusing for near vision, thepupil were moved to the position P1 Q1, nearer to .the

lens l (while the angnlarity of `the reectors remained constant) thecorresponding virtual imagek points Q11", reproduced by reflector 11,and P21, reproduced by reiectorV r2, would no longer coincide upon theaxis, but would be diswill be separated as shown. To bring these image yplaced in an overlapping relation as shown. Simvilarly, if the pupil ismoved away from the lens l to position -Pz Gb, in focusing for farvision, the corresponding virtual image points Q13 and P23" points intocoincidence for near and far vision requires a change in the angularityof the 'reiiectors; however, such a. change must not affect the scalewhich indicates the measure of the pupil f ofthe pupil at'iPz Q2 areshown in coincidence diameterf In the present invention this. isaccomplished by imparting to the reflector r1 a compensating movement`during the process of focusing, which automatically changes theangularity of the reflectors to cause the virtual image points to remainin their relation of coincidence` for all the intermediate positions ofthe pupil be-Y .tween near vision and far vision. The movement j ofthereflector r2 is however, controlled bythe- K 1 scale which indicates themagnitude of the pupil diameter, while the compensating movement of r1has no influence upon the indications' of this.`

scale. The eiect of this compensating movement is shown in Fig. 4. Theimage points Q11" P22" corresponding to the position of normal vision4vision the point of coincidence is of the axis, and

this requires a corresponding displacement of the centerofgtherpupil asshown at'Ag.' For far vision the compensated position Aoi? reector r1 isat n2 and the coincidence of the image 'points is at Q13" P23", off theaxis, but in the opposite direction to that for near vision. A: showsthe position of the center of the pupil for far vision. 5

Fig. 5 shows how the instrument is held relative ,to the eye. Thenose-piece I supported on a rod 2 which slides parallel to the axis ofthe lens l for varying the distance between the lens and the pupilvofthe eye 3.

The mechanism of the .device isbuilt on a frame member 4, Figs. 8, `11;12, 13 and. 14. The reectors r1 and r2, Figs. 8, Il yand 1 2 are mountedupon holders formed out of sheet metal, and are pivotally-supported uponthe frame member 4. An upwardly projecting portion 5, of the holder forreflector r1, is Yprovided with two bent hooks 6, at its upper end, andwith a similar hook I on its lower end, which is midway between the twoupper hooks, as shown in Figs. 10, 11' and 12.30

These hooks 6 and 'I provide a lthree point support for the reflector r1which is held in place against said hooks by a retaining spring 8, Fig.11. Below the left hand edge of the reector is a horizontal projectionprovidedwith a. hole s, 25 Fig. 10, by which said holder is pivotallysupported upon the pivot stud I0 o n the frame member 4, Fig. 11. On theright side. of the reflector holder an upwardly projecting part II(Figs. 8, 10, 11 and 12) is bent at rightangles toward the 30 left, asshown at I2, and is'provided with a hole I3, vertically above the lowerhole 9, Fig. 10. The frame member 4 is bent upward at I4, on the lefthand side, and a. s'hort portion I5 bent toward the right, Figs. 8, 11and 12. Portion l5 35 is provided with a pivot stud I 6 which isvertically above the lower pivot stud I Il.z The hole I3 in thereflector holder ts the pivot studv I6, so

that the reector holder is mounted for pivotal movement upon the twopivot studs 4III and IE. On the upper portion I2 of the reector holderis a YU shaped formation I1, provided. with an ad-` justing screw I8,(Figs. 8, 10'and 11) the end of which bears against the free upper endof the part 5 which supports the reflector, so that by 4.5 means of thisscrew the upper end of the reflector may be precisely adjusted, forobtaining the y proper positioning of the virtual images formed by thereflectors. 'Ihe lower part of the reflector holder extends rearwardlyand is provided with an upwardly bentl spring hook I9. Figs.l 8, 10 and11, and ending with a horizontal U formation 20, adapted to receive anadjusting screw 2|, Figs. 8, 11 and 14. The space between the parallelsurfaces of the U formation is some- 55 what less than the ldiameter ofthe screw, so that the screw threads are partially imbedded between theparallel surfaces. This type of adjusting screw takes up but littlespace in height and remains tight without a locknut. The re- 6o iectorholder for the reflector r2 is in' all respects similar to the reectorholder for the reiiector r1 with the exception of the lower rearwardprojection. Both reflector holders are supported by the same pivot studsI0 and IB, as shown in Figs. 65 11 and 12. The lower rearward projectionof. the reflector holder. for reector r2 is provided with a horizontal Uformation, similarto formation 2|), for receiving an adjusting screw 22,Figs.

8 and 13. 'I'he adjusting screw 22 bears against 7o a cam element v23,which'tsslidingly into the opening of the U formation as shown in Fig.13, and thereby insures the alignment of the adjusting screw in contactwith the cam.l To the rear of' the screw 22 the reflector holder /endsin a 13, on the two spring hooks, tends to rock the two reflectorholders about their pivots, and to hold the set screw 22 continuously incontact with the cam. 'I 'he cam is secured to a tubular extension of arevolving dial -wheel 25, Fig. 13, which is pivotally supported on a xedstud 21, and frictionally held by a resilient disc 28, Figs. 8 and 13,the circumferential part. of which presses o'n the bottom surface of acircular depression 29 of the dial wheel, while the central part of theresilient disc engages opposed slots 38, near the tcp of the stud 21.The inclined surface 3| of the dial wheel is provided with a scale, andsymbols or numbers which 'are read opposite a pointer 32, Fig. 5. Inplace of numerical values for the pupil diameters, the scale ispreferably graduated to indicate exposure periods in fractions of asecond; or arbitrary symbols on the dial may be referred to a table ofexposures, in which each symbol or division of the scale is corelated toa set of values corresponding to the varying factors (other than thelight intensity), which effect the time of exposure in photography.

sults from moving the pupil nearer or further from the lens I during theprocess of focusing.

Itcan be shown, however, that the overlapping or separation ofthe imagesis further effected by another factor, namely, the diameter of the pupilitself. The larger the diameter of the Vpupil the greater willbe theoverlapping or separation of the images, other conditions remain- Vingthe same. Hence, in order to obtain true compensation, it is necessaryto controlthe angular motion of the reiiector n not only by the distanceof the pupil from the lens l butV by the diameter 4of the pupil also.

w In Figs. a, 11, 12 and 13, a. channel shaped member 33 fits slidinglyinside the casing 34, and is supported' on its rearward end by an eX-tension 35, which is formed out of thev frame member, 4, Figs. 8 and 11.This extension 35 is Y provided with a slot 36, and a stud 31 sliding inthis slotis riveted to the channel member 33. By means of a frictionwasher 38, upon the stud 31, the member 33 is held in sliding frictionalcontact with extension 35. On the forward end,

`the channel member 33 is provided with lip 33,

and another4 similar lip is sheared out of the body of the member 33 at40, Figs. 8, 1l, l2 and 13. These spaced lips are provided with holesfor receiving the rod 2. Just inside thetwo lips the rod 2 is providedwith two grooves 4|, which are engagedfby the formed edges of aresilient ,which thenos piece l is mounted, the focusing movement istransmitted to the member 33. The

Vlower rearward end of the member 33,"is'provided with anv offsetprojection 44, Figs. 8 and 14, upon which is pivotally mounted a member45 by means of a stud 45. The member 45 is provided with a 1 cam surface.41, which 'cooperates I,with the end 'of the adjusting screw 2l, andthereby Iimparts The rod a compensating rocking motion to the reflectorn during the process of focusing. The tip of the screw 2| is maintainedin contact with thecam surface 41 by the spring 25. The member 45 has aforward extension 48 which bears against a cam 49, Figs. 8 and 13, whichis rigidly mounted upon the tubular extension of the dial wheel 26 belowthe cam`23, and is held in contact with this cam by the torsion spring50, Figs. 8 and 14. The dial wheel, through the cam 23, imparts arocking motion to reector rz which is definitely related to the member`33v is provided with two opposite finger pieces 5| and 52, which projectthrough vslots 53 in the casing 34, Figs. 5, 9, 11, 12, 13

and 14. The device is held by these iinger pieces with one hand, and thecasing grasped and moved with the other hand, sliding it upon the rod 2.'Ihe member 33-is provided with two rectangular apertures opposite theslots 53, through which the nger pieces are assembled. In Fig. 9 thefinger piece 5| .is shown with two slots, a short slot 54 and a'longerslot 55 opposite to the slot 54. The center of the longer slot is boredout to receive a compression spring 56, which exerts a Vpressure againstone side of the aperture in member 33, and forces the bottom of slot 54against the opposite side of the aperture. The spring 55 is stii enoughto hold the iinger piece 5| firmly relative to member 33 during theprocess of focusing. To remove the iinger piece, it is moved to compressthe spring 56 until the heel 51 clears the edge of the aperture, when'it can readily be tilted and removed; it is replaced in similar manner.

'I'he nose piece I, straddles the end of rod 2, Figs. 5, 8 and i1, andis held to the rqd by a stud 58, the head of which fits slidingly in ahole in the nose piece.. The stud is riveted to the rod 2 and a lightcompression spring 59. presses against the inside shoulder of the headof the stud and against a shoulder 60, near the bottom of the hole inthe nose piece. Thus the nose piece can be made to slide on the studagainst the tension of the spring 59 and thereby the optic axis shiftedrelative to the pupil, as explained in connection with pupil centers A1and A3, Fig. 4. Semicircular notches 6| are provided to hold the nosepiece iiatwise against the front wall 43, when the device is not in use,as shown in Fig. 6.

` 'Ihe adjusting screws 2| and 22 upon the re-. iiector holders are usedin the calibration of the instrument, in adjusting the angular relationbetween the reectors. It was explained that the pupil diameterscorresponding to a given light intensity, vary with differentindividuals, and therefore it is necessary to make a correctiveadjustment, adapting the instrument to the individual user. This canmost conveniently be done by adjusting the screw 2|, and in order tomake this easily accessible, means are provided for quickly and easilyremoving the casing 34. 'Ihe front wall 43 is rigidly fastened to, the

vertical part I4 of the framc'mernber 4, and the edge of the casing iitsagainst theinside edge of the wall v43 and closely about the peripheryof the part I4 as shown in Figs. 8 and 11.

'Ihe rearward end of the fram'e member 4 is bent upwardvat 62 upon whichis fastened a spring snap button 63 of conventional design,l lwhichcooperates with a snap stud 64 riveted into the rear wall 65, which ispart of the casing. Before the casing is pulled ofl. the snap button,the iinger pieces 5I and 452 xnust be removed.

'I'he nger pieces are preferably provided with a pointer 66 Fig. 5,which cooperates with a scale 61 alongside the slot 53. By setting thepointer opposite a predetermined division of the scale,

according t'o the visionof the individual user.

.` the necessity Afor repeated' focusing may be for moving the otherreilector, and means for indicating the magnitude of such motion.

2. In combination with an exposure meter, a lens, and means forpositioning said lens relative to the'pupil; two reflectors, adapted tore-v ect two distinct virtual images of the pupil; means for adjustingthe angle between said reflectors for shifting the images of -twodiametrically opposed points of the pupil into coincidence, and meansfor indicating the magnitude of said angle.

3. In combination with an exposure meter. a lens and means forpositioning said lens relative to the pupil; two reilectors, l andpivotal mountings for said reiectors; means for 1lmpart ing a rockingmovement to one of said reflectors,

the magnitude lof said rocking movemientA de#v pending upon the diameterof the pupil, and

means for indicating the magnitude of such mo-y tion; mechanism forimparting a rocking motiontothe other reflector, said motion beingsimultaneously dependent upon the positioning means for the lens andupon the diameter of the pupil. A

4. In combination with anexposure meter, a lens, and means forpositioning-said lens rela.-

tive to the pupil; two reectors, and pivotal' mountings forsaidreiiectors; a cam cooperating with one of-said reectors, and indicatorlmeans in connection with said cam; mechanism .confl Y nected with thepositioning means lof said lens for imparting a compensating movement tothe -other reflector. v

In combination with an exposure meter, a

lens, and means ior positioning said lens relative to the pupil; tworeectors, and pivotal mountings for said reile'ctors'," a dial wheel, acam integral with said dial wheel and cooperating with one of saidreflectors; another cam cooperating with the positioning means of saidlens, and adapted to impart movement to the other reector during theprocess of focusing.

6. In combination with an Ve'xposure meter, a lens, and means forpositioning said lens relative l0 to the pupil; two reflectors andpivotal mountings for said reflectors; a dial wheel; a camcooperatingwith one of said reflectors and integral with said-dialwheel; another cam pivotally supported upon the positioning means ofthelii lens, and adapted to impart motion to the other reector, andcooperative, connection between said camand the dial wheel. .v Y

'1. In combination with an'exposure meter, a lens, and means forpositioning. said-lens rela- 2.0. tive to the pupil; two reiiectois andpivotal mountings for said reectors; a cam cooperating with one of said'reectors and a screw for adjusting the position of the reilectorrelative to said cam; another cam connected to the posi-*25. tioningmeans for the lens and cooperatingwith the other reiiector, and av screwfor adiusting the position of said reiiector relative to the lastrecited cam.

8. In combination with an exposure meter, a 30 nose piecefor positioningthe device relative to the pupil; a support for said nose piece; a studupon said support, and means for mounting the nose piece `for slidingmotion upon said stud; a

spring for forcing the nose piece toward its 35- support, andcooperating means between the nose piece and its supporty for yieldinglysupporting the nose 'piece in two diil'erpnt positions'.

9. In combination with an exposuremeter. two reflectors; holders forsaid reectors adapted to be mounted on common pivots; a separate camcooperating with each of said reilector holders, and a spring forholding said holders in contact. with their cams. l

` 10. In combination with an exposure meter, a 15 lens, and means forpositioning said lens relative to the pupil of the human eye; tworeectors cooperating with said lens,'for viewing two sepvarate 'imagesof the pupil; a pivotal mounting for one of the reflectors; a cam; andmeans for `5 imparting a tilting movement, to the pivoted reiiector bythe operation of said cam, for tilting said reector relative to theother reflector, vto bring the images of the4 pupil into a predeterminedalignment, and ascale device cooperating 55 with said cam, forindicating the magnitude of said tilting movement.

,- NICHOLAS MILLER.

